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A Westchester County dentist was on his way to a convention when his train derailed near the Spuyten Duyvil station. Marc Santia has more of the harrowing sights and sounds from a man who walked away from the deadly crash. (Published Monday, Dec. 2, 2013)

The Metro-North train that derailed in the Bronx on Sunday, tossing passengers out windows and sending cars sliding down a bank, was going 82 mph as it entered a curve where it should have been going 30 mph, investigators said.

Four people were killed and dozens more were injured when the first four cars of the seven-car train broke away as the train was about 100 yards north of the Spuyten Duyvil station.

NTSB member Earl Weener said at a briefing Monday that the data on the train's speed were pulled from preliminary reviews of the train's black box. Investigators have also learned from the black box that the throttle went idle six seconds before the crash, and the brake pressure went to zero, indicating "full application of the brakes."

There was so far no indication of a problem with the brakes, Weener said.

Photos: Deadly NYC Train Derailment

As to whether human or mechanical error caused the train to be hurtling down the tracks at such a high speed, Weener said it was too early to know the cause.

"That's the question we need to answer," he said.

The NTSB has already begun interviewing the crew members and reviewing the engineer's cell phone, which Weener said was part of the forensic process. Technicians were also working to enhance poor surveillance video of the crash that was taken from a nearby bridge.

The engineer told first responders on the scene that he tried to apply the brakes to slow the train before the curve, one of the sharpest on the line, but the brakes failed, several senior officials told NBC 4 New York.

Anthony Bottalico, the chairman of the train engineer's union, ACRE Local 1, said the engineer was "traumatized" by the derailment and "distraught over the loss of life."

The Bronx district attorney is also involved in the investigation, a spokesman said.

Meanwhile Monday, a hospital that received some of the injured said nine of the 12 people brought there remain hospitalized, seven in intensive care. One is still critical. Another hospital said it still has two people in critical condition, and five others being treated.

The people killed were identified as Jim Lovell, 58, of Cold Spring, N.Y.; James Ferrari, 59, of Montrose, N.Y.; Donna Smith, 54, of Newburgh, N.Y., and Ahn Kisook, 35, of Queens. Eleven people were critically hurt, including a 43-year-old man with spinal cord injuries.

One of the passengers on board said he didn't notice anything out of the ordinary before the derailment.

"There was absolutely nothing suspicious happening on the train," said Steven Ciccone, who was traveling from a Thanksgiving celebration. "All of a sudden it started to shudder, and then it started to slip."

Passenger Dennis O'Neil said he thought the train was going too fast before it crashed, throwing him against the window.

"It was coming towards Spuyten Duyvil and you could feel it starting to lean and it was like 'hey what's going on,' and then it hit the curb real hard and flopped over and slid down the hill," said O'Neil. "A couple people were hurt very badly right in front of me."

In July, a CSX freight train hauling trash derailed in the same area, near the Spuyten Duyvil station, due to a track issue. Nobody was injured in that derailment, and officials said Sunday that they do not believe this latest crash was related to the July derailment. This is the second passenger train derailment on Metro-North in six months.